1. Field of the Invention
The present invention relates to a fuel supply apparatus which is mounted in a fuel tank and is operative to stably supply fuel to an internal combustion engine, and more particularly, to a fuel supply apparatus of the type in which a fuel pump body is disposed in abutment with the bottom side of the fuel tank.
2. Description of the Related Art
In the field of fuel tanks used for supplying fuel to internal combustion engines such as automotive engines, a fuel supply apparatus has heretofore been known which is constructed to ensure stable operation of a fuel pump even when the liquid level in the fuel pump varies, by making use of a subtank in which the fuel pump is accommodated.
For example, a fuel supply apparatus of the type in which a fuel pump body is mounted on the bottom side of a fuel tank is disclosed in JP-A-11-294282 (Patent Document 1, FIG. 3).
FIG. 12 schematically shows the fuel supply apparatus of Patent Document 1, and this fuel supply apparatus will be described below. Referring to FIG. 12, a filter-integrated pump 103 in which a fuel pump unit 101 and a fuel filter unit 102 are integrally formed is fixedly accommodated integrally with a suction-side filter 104 in a rotary tank 108 having a flat bottom capable of coming into abutment with the bottom side of a fuel tank (not shown), and a rotary-tank mounting wall 122 capable of being fitted into the integrated rotary tank 108 is provided on a fuel tank lid 119 through which a fuel discharge passage portion 120 is inserted. The rotary-tank mounting wall 122 and the rotary tank 108 are expansibly fitted together by an expanding/shortening mechanism 138.
The rotary-tank mounting wall 122 is constructed so that its inside diameter becomes approximately equal to or slightly greater than the outside diameter of the filter-integrated pump 103 and its outside diameter becomes approximately equal to or slightly smaller than the inside diameter of the rotary tank 108, whereby the rotary-tank mounting wall 122 can be inserted into the gap between the filter-integrated pump 103 and the rotary tank 108. In addition, guide tube portions 124 which extend in an axial direction 113 are formed in the inside of the rotary tank 108 at a plurality of circumferential positions thereof, and guide portions 125 capable of being slidably fitted into the respective guide tube portions 124 are formed at the corresponding positions of a side portion of the rotary-tank mounting wall 122. An elastic member 126 such as a coiled spring is interposed between the guide tube portions 124 and the guide portions 125 to expansibly support the rotary-tank mounting wall 122 and the rotary tank 108 by the elastic force of the elastic member 126.
Furthermore, engaging claw portions 127 are respectively formed at a plurality of circumferential positions of a side portion of the rotary-tank mounting wall 122, and a plurality of engaging slots 128 which extend in the axial direction 113 to movably receive and hold or engage and hold the respective engaging claw portions 127 are formed at the corresponding positions of the rotary tank 108.
The discharge port of the fuel pump unit 101 and the inlet of the fuel filter unit 102 are connected to each other by means of a flexible tube 105, and the outlet of the fuel filter unit 102 is connected to another flexible tube 107 having a joint 106 at its extending end, whereby fuel in which foreign matter has been filtered out is supplied to an internal combustion engine such as an automotive engine via the fuel discharge passage portion 120.
The fuel supply apparatus of Patent Document 1 is placed in abutment with the bottom side of the fuel tank, but if the fuel tank is formed of, for example, a molded resin product, the fuel tank is inferior in dimension accuracy and is easily deformed by the influence of the fuel temperature inside the fuel tank. This leads to the problem that since the position of the bottom side of the fuel tank easily varies so that the liquid level of the fuel easily varies, it is difficult to ensure stable operation of the fuel pump. It is to be noted that the fuel supply apparatus is formed to expand and shorten by means of the urging force of an elastic member such as a coiled spring, but in the case where the amount of deformation of the fuel tank is large, the degree of freedom of spring design such as spring constant becomes low in that such deformation cannot be easily absorbed by only the elastic member such as a coiled spring, so that the accuracy of the elastic member to follow the deformation is limited.
In addition, the fuel supply apparatus of Patent Document 1 is constructed in such a manner that the guide tube portions 124 are formed in the inside of the rotary tank 108 and the guide portions 125 capable of being fitted into the respective guide tube portions 124 are formed on the side portion of the rotary-tank mounting wall 122, and the elastic member 126 such as a coiled spring is interposed between the guide tube portions 124 and the guide portions 125 to expansibly support the rotary-tank mounting wall 122 and the rotary tank 108 by the elastic force of the elastic member 126. This construction entails a complicated structure and an increase in manufacturing cost due to an increase in the number of component parts. Furthermore, the setting of the elastic modulus of the coiled spring needs to be made variously different for different uses, and in addition, the fatigue of the spring itself must be taken into account. Accordingly, it is extremely difficult to design a fuel supply apparatus which can stand up to long hours of practical use.
In addition, the fuel supply apparatus of Patent Document 1 has the problem of being inferior in ease of assembly in the fuel tank. Namely, during the assembly of a fuel tank lid unit, first of all, the filter-integrated pump 103 is accommodated into the rotary tank 108, and the filter-integrated pump 103 and the rotary tank 108 are integrated with each other with the distance between the suction port of the fuel pump unit 101 at the bottom of the filter-integrated pump 103 and the bottom of the rotary tank 108 held at a predetermined value by engaging dent grooves provided in the rotary tank 108 with receiving members provided on the filter-integrated pump 103 and by engaging hole portions provided in the rotary tank 108 with engaging claw portions provided on the filter-integrated pump 103.
Furthermore, the joint 106 provided at the extending end of the flexible tube 107 is connected to the inside end of the fuel discharge passage portion 120 inserted through the fuel tank lid 119, and although not shown, a joint provided at an extending end of a flexible tube is connected to an inside end of a fuel return passage portion which is inserted through the fuel tank lid 119, and during this state, the rotary-tank mounting wall 122 is inserted into the gap between the filter-integrated pump 103 and the rotary tank 108. At this time, the respective guide portions 125 are slidably fitted into the guide tube portions 124 formed at the plurality of circumferential positions in the inside of the rotary tank 108 with the elastic member 126 such as a coiled spring inserted therebetween. Accordingly, the fuel supply apparatus of Patent Document 1 is complicated in assembly and inferior in operability.